It is known to determine the straightness of a profile workpiece, an I-beam for example, by placing a support bar on its flange and to measure the straight line relative to a spanned wire. Such manual measurement takes a lot of time and, because it cannot normally be done while the process is running, leads to down time and production losses.
For automated measurement and determination of the straightness of rails and profiles on a continuously passing workpiece, it is known from the prior art to utilise laser measuring devices and/or methods. In doing so, the rail is moved across a roller bed at approximately 1 m/s and the spacing between the laser head and the rail is measured. This procedure makes it possible to determine the waviness (straightness only along short distances, e.g. 1 m). This system, a so-called optical ruler, combines multiple simultaneous position measurements at multiple points in relation to the optical-ruler reference. This laser-measurement method becomes much less effective at higher speeds, for example 10 m/s, because the actual movement of the profile or elongated workpiece, such as bouncing on the roller table or oscillations, distorts the measured result, creating a disturbance variable that greatly reduces the accuracy of the measurement obtained.
A different measurement method and apparatus is disclosed in EP 0 935 120. In it, the straightness of an elongated workpiece is ascertained using multiple weight sensors spaced along the workpiece. The elongated workpiece is contacted at defined points and the workpiece weight is determined at each point. The weight varies longitudinally due to the shape of the long material or workpiece or its curvature, so that the straightness can be ascertained therefrom. Such a system can however only be used in continuous pass-through under limited conditions. In addition, the friction and other effects resulting from contact with the underlying roller table are undetermined and make the readings less accurate.